With respect to a method for manufacturing a solid fuel using a porous coal, such as brown coal, as a starting material, the manufacturing method described in Patent Document 1 has been conventionally known. The method for manufacturing a solid fuel described in Patent Document 1 is characterized by mixing a mixed oil including a heavy oil component and a solvent oil component with a porous coal to obtain a starting material slurry, heating the slurry to dewater the porous coal and to impregnate the pores of the porous coal with the mixed oil including the heavy oil component and the solvent oil component, and then solid-liquid separating and drying the slurry.
In the method for manufacturing a solid fuel described in Patent Document 1, moisture in the pores of the porous coal is evaporated by heating the starting material slurry (i.e., mixture of the mixed oil including a heavy oil component and a solvent oil component with the porous coal). At the same time, the inside of the pores is covered with the mixed oil including the heavy oil component. Finally, the pores are filled with the mixed oil, in particular, the heavy oil component preferentially. Consequently, adsorption of oxygen to active sites in the pores and oxidation are suppressed, and thus spontaneous combustion of the porous coal is suppressed. Furthermore, the heavy oil component is filled in the pores by the heating, resulting in an increase in the calorific value of the porous coal. Hence, according to the method for manufacturing a solid fuel described in Patent Document 1, it is possible to obtain a solid fuel having a low moisture content, low spontaneous combustibility, and an increased calorific value.
However, in the method for manufacturing a solid fuel described in Patent Document 1, since the modified coal (solid fuel) after being subjected to the drying step is in powder form, a problem occurs with respect to its transportation. Specifically, use of the modified coal in powder form may result in an increase in transportation costs and may cause dust pollution because of the low bulk density, leakage during transportation, and fly loss. Consequently, it is desirable to briquette the modified coal in powder form using a briquetting machine. In this process, the modified coal in powder form cannot be briquetted unless under high pressure. Therefore, it has been a problem to reduce the briquetting cost. Note that, if the strength of briquettes is not high enough, the briquettes will be easily pulverized during handling.
As the technique for briquetting a modified coal in powder form, for example, the method for manufacturing a briquette coal described in Patent Document 2 has been conventionally known. In the manufacturing method described in Patent Document 2, starch is added to a coal in powder form, mixing is performed, and the resulting mixture is briquetted under pressure. That is, in this method, starch is used as a binder.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 7-233383    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-64377